1. Technical Field
The present invention relates generally to wireless communication and in particular, to a mobile radio telephone capable of recording and reproducing received frame data of voice channels.
2. Description of the Related Art
In general, a digital mobile communication system has advantages over analog systems both in terms of more efficient use of the frequency spectrum and superior speech quality. Digital mobile communication systems can be generally divided into GSM (Global Systems for Mobile Communication) systems and CDMA (Code Division Multiple Access) systems. The IS-95 (Interim Standard-95) DS/CDMA system has been adopted in both Korea and in the U.S.A. for applications such as PCS (Personal Communication Systems) and digital mobile radio communication systems.
In a mobile radio communication system employing the IS-95 DS/CDMA standard, a transmitter encodes voice data using a vocoder (i.e., a voice coder and decoder) and then converts the encoded data into a frame format having a plurality of data rates. For example, the vocoder in a transmission section of an IS-95 DS/CDMA system can set the data rate of the voice signal to one of the following data rates according to the voice traffic per unit time: full data rate, ½ rate, ¼ rate, and ⅛rate. The frame format of the voice data is 20 ms irrespective of the selected data rate. The vocoder of the transmitting party selects a data rate on the basis of the voice signal activity per unit time. A base station changes the length of the data packet within a frame according to the variable data rate, thereby transmitting the frame data.
Mobile radio telephones employing the IS-95 DS/CDMA standard are manufactured and sold by a plurality of communication equipment manufacturers such as QUALCOMM, MOTOROLA and SAMSUNG.
Mobile radio telephones employing the DS/CDMA system detect the frame data rate for a current voice channel by detecting a format byte contained within the frame data of a forward traffic voice channel. Having detected the data rate, the mobile radio telephone then decodes encoded voice data in accordance with the detected data rate. The vocoder of the mobile radio telephone decodes an information bitstream as part of a data packet within the received frame data as a PCM (Pulse Code Modulation) voice sample in accordance with a QCELP (QUALCOMM Codebook Excited Linear Prediction) algorithm. The voice data which is decoded as a PCM voice sample by the vocoder is reproduced as an analog voice signal by a PCM codec and is converted into an audible signal by a speaker.
While the general mobile radio telephone is capable of processing both the voice signal of the forward traffic channel and the voice signal of a reverse traffic channel, it is not capable of recording and reproducing voice messages transmitted from a communicating party (i.e., memo function). For example, in the case where a telephone number is provided from a transmitting party, the user must inconveniently manually record the number as it is spoken otherwise, the information is lost.
Thus, there is a need for a mobile radio telephone capable of recording and reproducing voice messages transmitted from a communicating party.